This invention relates to buffered phosphorus containing solutions, including such fertiliser solutions and including such fungicidal solutions.
The use of phosphorous acid and phosphites instead of phosphoric acid and phosphates as fertilisers and/or fungicides are known. Phosphorous acid and phosphites have the advantage over phosphates in that they are more readily absorbable by the foliage of plants such as citrus and avocado plants. Another advantage is that phosphites have fungicidal properties in addition to their fertilising properties.
Accordingly phosphite compositions in an unbuffered form have been marketed for foliage uptake and for applications to the soil. These compositions are sold as concentrated solutions that have to be diluted with water prior to application. It will be appreciated that the pH of the water used during dilution will have an influence on the pH of the diluted solution. In some cases the quality of the water may be such that the pH of the diluted solution may be influenced to such an extent that it falls outside the range where the diluted solution is suitable to be taken up by foliage. The pH range, which is acceptable for the solution to be taken up by the plant foliage, differs from one plant type to another, but usually it is from a pH of about 5 to a pH of about 7.
U.S. Pat. No. 4,075,324 describes fungicidal compositions containing phosphorous acid, inorganic and organic salts thereof.
U.S. Pat. No. 5,514,200 describes a buffered fertiliser composition comprising an organic acid and salts thereof and a phosphorous containing acid and salts thereof, which upon dilution forms a substantially fully solubilised fertiliser having a foliage acceptable pH for phosphorous uptake. The patent accordingly teaches how to overcome the above disadvantage. The patent teaches that the fertiliser comprises a double or multiple buffer systems that stabilise the phosphorous species against oxidation to phosphate. It further claims that the properties of phosphite that make it desirable as a fertiliser are enhanced when formulated as a double or multiple buffer according to the invention. Furthermore it is claimed that increased solubility of the formulation is obtained and that greater uptake of phosphorous is achieved.
It is an object of the present invention to provide an alternative buffered phosphorus containing solution, especially to such solutions for application to plants.
According to the present invention there is provided a buffered phosphorus containing solution containing at least one phosphorus compound selected from the group consisting of phosphorous acid, hypophosphorous acid, polyphosphorous acid, polyhypophosphorous acid, and salts thereof; and a buffer including an organic base in the form of a nitrogen containing compound and is conjugate acid.
It will be appreciated that since the phosphorus containing solution is in fact a solution the phosphorus compound will usually be dissolved therein.
Preferably the solution comprises an aqueous solution.
The solution may comprise a concentrated solution of the phosphorus compound. Preferably the solution has a concentration from 2 mol.dmxe2x88x923 to 8 mol.dmxe2x88x923 of the phosphorus compound More preferably the concentration is from 4.5 mol.dm31 3 to 7.5 mol.dmxe2x88x923. Most preferably the concentration is about 6.8 mol.dmxe2x88x923.
The phosphorus compound preferably comprises phosphorous acid and/or a salt thereof. Most preferably it comprises a salt of phosphorous acid. Preferably it comprises an alkali metal salt or an alkaline earth metal salt of phosphorous acid. Most preferably it comprises a potassium salt of phosphorous acid.
The salt of the phosphorous acid may comprise a monosubstituted and/or disubstituted phosphorous acid. Preferably it comprises a mixture of mono-and disubstituted phosphorous acid. Preferably it comprises a mixture of KH2PO3 and K2HPO3. Preferably the monosubstituted phosphorous acid is present in a larger molar amount than the disubstituted phosphorous acid. Preferably the molar ratio between the mono and disubstituted phosphorous acid is from 4:1 to 3:1. Preferably it is about 3.3:1.
The salt of phosphorous acid may be prepared by reacting phosphorous acid with a suitable base. Preferably the base is added in such an amount to provide the solution at a pH suitable for foliar uptake. Usually this is at a pH from about 5 to about 7. Preferably the pH is from about 6 to 7. Most preferably the pH is about 6.5.
The salt may be prepared by first reacting phosphorous acid with a first base (such as potassium carbonate) and thereafter reacting it with another base (such as KOH). The first base may comprise a compound which does not include hydroxide, preferably it is a carbonate, and preferably it is an alkali metal carbonate. The other base may comprise a hydroxide containing compound, preferably an alkali metal hydroxide. The first base may be a weaker base than the second base. It is believed that the addition of a salt such as potassium carbonate increases the solubility of the phosphorous acid salt. By using potassium carbonate to first react with phosphorous acid, a solubility of 550 g/l phosphorous acid was obtained which is much higher than previous obtained concentrations.
The buffer may be prepared by mixing the organic base in the form of the nitrogen containing compound with an inorganic acid, preferably a mineral acid.
The nitrogen containing compound may comprise a heterocyclic compound containing at least one nitrogen atom as a ring member, preferably two nitrogen atoms as ring members. The ring may comprise from 5 to 6 members, but preferably it comprises 5 members. Preferably the heterocyclic compound is aromatic. In a most preferred embodiment of the invention the heterocyclic compound comprises imidazole.
The mineral acid may comprise hydrochloric acid, sulphuric acid or nitric acid Preferably it comprises hydrochloric acid.
The buffer preferably buffers the solution at a pH suitable for foliar uptake. Usually this is at a pH from about 5 to about 7. Preferably the pH is from about 6 to 7. Most preferably it is about 6.5.
The buffer comprising imidazole and its salt formed with hydrochloric add is a very effective buffer and relatively small amounts of the buffer can be used. The pH at which the solution is buffered can also be adjusted by adjusting the molar ratio of the imidazole and hydrochloric acid used to form the salt.
The organic base forming the buffer may be present at a concentration from 0.03 mol.dmxe2x88x923 to 0.07 mol.dmxe2x88x923. Preferably from 0.045 mol.dmxe2x88x923 to 0.055 mol.dmxe2x88x923, and preferably about 0.05 mol.dmxe2x88x923.
A wetting agent may also be included in the phosphorus containing solution.
Additional plant nutrients, such as a source of nitrogen may also be added. The nutrient may comprise urea, ammonium nitrate, potassium nitrate, magnesium nitrate, and calcium nitrate. It will be appreciated that the nitrogen containing base such as imidazole may also serve as a source of nitrogen.
The phosphorus containing solution may be for treating plants. In one embodiment of the invention the phosphorus containing solution may be a fertiliser solution.
In another embodiment of the invention the phosphorus containing solution may comprise a fungicide. Preferably it comprises a fungicide suitable for use against Oomycetes, preferably for use against Peronosporales, preferably for use against Phytophthora and Pythium species.
According to another aspect of the present invention there is provided a method of preparing a buffered phosphorus containing solution comprising the step of mixing together:
at least one phosphorus compound selected from the group consisting of phosphorous acid, hypophosphorous acid, polyphosphorous acid, polyhypophosphorous acid, and salts thereof;
water; and
an organic base in the form of a nitrogen containing compound and its conjugate acid to buffer the solution.
Preferably the phosphorus compound comprises a salt of phosphorous acid. The salt of phosphorous acid may be prepared by reacting phosphorous acid with a suitable base. Preferably the base is added in such an amount to provide the solution at a pH suitable for foliar uptake. Usually this is at a pH from about 5 to about 7. Preferably the pH is from about 6 to 7. Most preferably the pH is about 6.5. The salt may be prepared by first reacting phosphorous acid with a first base (such as potassium carbonate) and thereafter reacting it with another base (such as KOH). The first base may comprise a compound which does not include hydroxide, preferably it is a carbonate, and preferably it is an alkali metal carbonate. The other base may comprise a hydroxide containing compound, preferably an alkali metal hydroxide. The first base may be a weaker base than the second base. It is believed that the addition of a salt such as potassium carbonate increases the solubility of the phosphorous acid salt. The phosphorous acid may be reacted with the suitable base in the presence of water.
The invention also relates to the use of a phosphorus containing solution substantially as described hereinabove for treating plants or a locus especially a locus where plants are cultivated or to be cultivated. The solution may be used as a fungicide. Alternatively or additionally the solution may be used as a fertiliser. The solution may be applied directly to the plants, for example by spraying the plants or by drenching their roots, but preferably by applying it to the foliage of the plants. The solution may also be injected into plant, preferably into the stems, of plants.
The invention also relates to a method of treating a plant or a locus comprising applying to the plant or locus a phosphorus containing solution substantially as described hereinabove.